Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in, e.g., disc form, such as utilized in computer-related applications, comprises a non-magnetic, disk-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al—Mg), having at least one major surface on which a layer stack or laminate comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni—P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr—V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material, e.g., diamond-like carbon (“DLC”) having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate typically comprises a reflective layer, e.g., of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more transparent dielectric layers, and a protective overcoat layer, e.g., a DLC layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Thin film magnetic and MO media in disk form, such as described supra, are typically lubricated with a thin topcoat film or layer comprised of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear of the disc when utilized with data/information recording and read-out transducer heads operating at low flying heights, as in a hard disk system functioning in a contact Start/Stop (“CSS”) mode. Conventionally, the thin film of lubricant is applied to the disc surface(s) during manufacture by dipping into a bath containing a small amount of lubricant, e.g., less than about 1% by weight of a fluorine-containing polymer, dissolved in a suitable solvent, typically a perfluorocarbon, fluorohydrocarbon, or hydrofluoroether.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (“CSS”) cycle commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk, and stopping.
It is considered desirable during reading and recording operations, and for obtainment of high areal recording densities, to maintain the transducer head(s) as close to the associated recording surface(s) as is possible, i.e., to minimize the “flying height” of the head(s). Thus a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk surface to be positioned in close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the head during motion.
The lubricity properties of disk-shaped recording media are generally measured and characterized in terms of dynamic and/or static coefficients of friction. The former type, i.e., dynamic friction coefficient, is typically measured utilizing a standard drag test in which the drag produced by contact of a read/write transducer head with a disk surface is determined at a constant spin rate, e.g., 1 rpm. The latter type, i.e., static coefficients of friction (also known as “stiction” values), are typically measured utilizing a standard contact start/stop (“CSS”) test in which the peak level of friction is measured as the disk starts rotating from zero (0) rpm to a selected revolution rate, e.g., 5,000 rpm. After the peak friction has been measured, the disk is brought to rest, and the start/stop process is repeated for a selected number of start/stop cycles. An important property of a disk which is required for good long-term disk and drive performance is that the disk retain a relatively low coefficient of friction after many start/stop cycles or contacts with the read/write transducer head, e.g., 20,000 start/stop cycles.
The most commonly employed lubricants utilized with thin film, disk-shaped magnetic and MO media, i.e., perfluoropolyether (“PFPE”)-based lubricants, perform well under ambient conditions but not under conditions of higher temperature and high or low humidity. Studies, as described in, for example U.S. Pat. No. 5,587,217, the entire disclosure of which is incorporated herein by reference, have indicated that the tribological properties, and perhaps corrosion resistance, of perfluoropolyether-based lubricants utilized in the manufacture of thin film recording media can be substantially improved by addition thereto of an appropriate amount of a cyclotriphosphazene-based lubricant additive, e.g., a polyphenoxy cyclotriphosphazene comprising substituted or unsubstituted phenoxy groups, to form what is termed a “composite lubricant”.
Currently, bis (4-fluorophenoxy)-tetrakis (3-trifluoromethyl phenoxy) cyclotriphospazene (available as X-1P™ from Dow Chemical Co., Midland, Mich.) is the additive most commonly utilized with perfluoropolyether-based lubricants for forming composite lubricants for use with thin film magnetic and MO media. However, as disclosed in U.S. Pat. Nos. 5,718,942 and 5,908,817, the disclosures of which are incorporated herein by reference, the use of X-1P as a lubricant additive for forming composite lubricants comprising the perfluoropolyether-based lubricants commonly employed in the data storage industry (e.g., Fomblin Z-DOL™ and Fomblin Z-TETRAOL™, each available from Ausimont, Thorofare, N.J.) incurs a disadvantage in that the former (i.e., the cyclotriphosphazene-based lubricant additive) has very low solubility in the latter (i.e., the PFPE-based primary lubricant).
For example, X-1P, in combination with Z-DOL at levels up to about 5 wt. %, reduces stiction and increases the stability of Z-DOL. However, because X-1P is virtually immiscible in PFPE-based lubricants, phase separation typically occurs at the optimal X-1P/PFPE ratios. The phase separation leads to chemical non-uniformity of the lubricant film on the media (e.g., disk) surface, as by the so-called “balling” effect, which tends to affect the tribology (i.e., durability) of the head/disk interface, particularly when the thickness of the X-1P exceeds about 1-2 Å. As a consequence of the poor compatibility of the X1P lubricant additive with the Z-DOL or Z-TETRAOL primary lubricant, the maximum amount of X-1P that can be used therewith is limited by the PFPE type and carbon type of the protective overcoat layer. Thus, according to current practice, the effective concentration window for use of X-1P in combination with PFPE is quite narrow, and special process control is required to achieve optimal performance. Notwithstanding such special process control, phase separation of the X-1P additive, accelerated lubricant loss, and a large amount of transducer head smear frequently occur even with such low additive contents.
U.S. Pat. No. 6,099,762, the entire disclosure of which is incorporated herein by reference, discloses a process for enhancing the bonding, thus durability, of thin lubricant layers comprised of a PFPE, a phosphazene, or both, to media surfaces by means of a process comprising exposing the lubricant layer or film to infra-red (“IR”) and ultra-violet (“UV”) radiation, either simultaneously or sequentially, wherein the IR radiation effects heating of the lubricant layer or film to a temperature above about 150° F. but less than about 500° F., and the UV radiation comprises a wavelength component of about 185 nm for photolytically generating ozone (O3) in the vicinity of the lubricant layer or film for effecting bonding thereof to the media surface. This process for enhancing bonding of the composite lubricant films to the media surface, however, is not performed in a manner as to effect optimal stabilization of the composite lubricant films and enhancement of their durability when utilized in CSS-type operation.
Co-pending U.S. Pat. No. 6,686,019 filed Nov. 13, 2001 and application Ser. No. 10/106,486 filed Mar. 27, 2002, each assigned to the assignee of this application, disclose methods for treating thin films or layers of composite lubricant, such as Z-DOL PFPE/X-1P composite lubricants, solely with UV radiation for effecting curing thereof for, inter alia, stabilization against phase separation and improved tribological performance. However, inasmuch as the efficiency of the UV curing process affects product throughput in automated manufacturing of data/information storage and retrieval media, e.g., magnetic and/or MO disks, it is considered important to minimize the UV irradiation dosage while maintaining the improved performance characteristics afforded by the UV curing process.
In view of the above, there exists a clear need for improved methodology for forming thin films of lubricants, such as, for example, composite lubricant materials, on surfaces of thin film recording media, e.g., in disk form, which methodology overcomes the drawbacks and disadvantages described above, particularly with respect to efficiency of the UV curing process. More specifically, there exists a need for improved methodology for applying and treating lubricant thin films utilized in the manufacture of thin film magnetic and/or MO recording media, e.g., lubricant materials comprised of a primary lubricant and a lubricant additive for enhancement of the stability, durability, and tribological properties of media which operate under CSS conditions.
The present invention addresses and solves problems and difficulties in efficiently performing UV irradiation processing for achieving stabilized, high performance, high durability lubricant thin films in the manufacture of thin film, disk-shaped magnetic and MO data/information storage and retrieval media for operation under CSS conditions, for example, wherein the lubricant thin films are comprised of a primary lubricant and a lubricant additive, while maintaining fill compatibility with all aspects of conventional automated manufacturing technology therefor, including productivity requirements necessary for economic competitiveness. In addition, the present invention provides improved thin film magnetic and MO media having stabilized, high durability lubricant films, e.g., composite lubricant thin films comprised of a primary lubricant and a lubricant additive. Further, the methodology afforded by the present invention enjoys diverse utility in the manufacture of various other devices and/or articles requiring formation of stable, high performance lubricant thin films thereon.